This invention relates to a circuit and system for doubling the level of voltage applied to fuel injectors. High performance fuel injectors often require excitation voltages in excess of battery voltage. To achieve this higher voltage, voltage doubler circuits have been used. In a four-cycle engine, which requires fuel injector firing once such two revolutions of the engine, the time available for generating the increased voltage is relatively long. The present invention has been developed for use with engines such as a two-cycle engine in which each injector must fire once per revolution. As such, the luxury of the longer time period of the four-cycle engine is not available. The present invention defines a voltage doubler circuit for a single injector as well as a system employing two voltage doubler circuits which are alternatingly actuated to activate a plurality of fuel injectors arranged in a like plurality of groups. The voltage doubler circuits are capable of generating the increased voltage during the time of peak injector current flow yielding a maximum charge-time for associated capacitors. Such timing and the alternately generation of the charge-time permits overlapping control pulses to be handled easily.
An object of the present invention is to generate a doubled excitation voltage in a relatively short time. A further object of the invention is to control the excitation of a number of fuel injectors with a lesser number of voltage doubler circuits.
Accordingly the invention comprises: a circuit for energzing at least one fuel injector comprising: a voltage doubler circuit connected to a voltage source (B+) and including a charge storage capacitor (C.sub.S), means operative during a first mode for causing the storage capacitor to charge to substantially the voltage level of the voltage source and means operative during a second mode from connecting the voltage source and storage capacitor in series; first means in circuit with the fuel injector and the voltage doubler circuit for: selectively completing a current path through the injector to enable and disable current flow therethrough in response to an input control signal, and for regulating the magnitude of the current flowing through the injector to a hold or steady state level; second means responsive to the input control signal and the magnitude of current in the injector for generating a first control signal, the first control signal characterized that during intervals prior to the input control signal such first control signal is maintained in a first state sufficient to cause the voltage doubler circuit to be in its first mode, and during intervals subsequent to the input control signal such first control signal is maintained in a second state sufficient to cause the voltage doubler circuit to be in its second mode. The second means including means for returning the first control signal to its first state after the level of current has reached a predetermined peak level to thereby reset the voltage doubler circuit to its first mode immediately thereafter.